EducationBot: Новая страница: «{{Английская Википедия/Панель перехода}} {{short description|Type of hyperlink}} A '''canonical link element''' is an HTML element that helps webmasters prevent duplicate content issues in search engine optimization by specifying the "canonical" or "preferred" version of a web page. It is described in RFC 6596, which went live in April 2012.{{Cite web|url=https://goo...»

2024-02-14T13:20:23Z

Новая страница: «{{Английская Википедия/Панель перехода}} {{short description|Type of hyperlink}} A '''canonical link element''' is an HTML element that helps webmasters prevent duplicate content issues in search engine optimization by specifying the "canonical" or "preferred" version of a web page. It is described in RFC 6596, which went live in April 2012.<ref name="googleblog">{{Cite web|url=https://goo...»

Новая страница

{{Английская Википедия/Панель перехода}}
{{short description|Type of hyperlink}}
A '''canonical link element''' is an [[HTML element]] that helps [[webmasters]] prevent [[duplicate content]] issues in [[search engine optimization]] by specifying the "[[Canonicalization|canonical]]" or "preferred" version of a web page. It is described in RFC 6596, which went live in April 2012.<ref name="googleblog">{{Cite web|url=https://googlewebmastercentral.blogspot.com/2009/02/specify-your-canonical.html|title=Specify your canonical|last=Kupke|first=Joachim|date=2009-02-12|website=|publisher=Google|archive-url=|archive-date=|accessdate=2012-08-02}}</ref><ref>{{Cite web|url=https://www.mattcutts.com/blog/canonical-link-tag/|title=Learn about the Canonical Link Element in 5 minutes|last=Cutts|first=Matt|authorlink=Matt Cutts|date=2009-02-15|website=|archive-url=|archive-date=|accessdate=2012-08-02}}</ref>

== Purpose ==

A major problem for [[search engines]] is to determine the original source for documents that are available on multiple [[URL|URLs]]. Content duplication can happen in many ways, including:<ref name="Audisto GmbH">{{Cite web |url=https://audisto.com/insights/guides/28/ |title=Link rel=canonical: How to do URL canonicalization right |accessdate=2015-10-06 |publisher=Audisto GmbH | authorlink= Tobias Schwarz & Christian Mueller}}</ref>

* Duplication due to [[query string|{{mono|GET}}-parameters]]
* Duplication with multiple URLs due to [[content management system|CMS]]
* Duplication due to accessibility on different hosts/protocols
* Duplication due to print versions of websites

Duplicate content issues occur when the same content is accessible from multiple [[URL]]s.<ref>{{Cite web|url=https://support.google.com/webmasters/answer/66359|title=Duplicate content|last=|first=|date=|website=|publisher=Google|archive-url=|archive-date=|accessdate=2012-08-02}}</ref> For example, {{mono|<nowiki>http://www.example.com/page.html</nowiki>}} would be considered by [[search engines]] to be an entirely different page from {{mono|<nowiki>http://www.example.com/page.html?parameter=1</nowiki>}}, even though both URLs may reference the same content.<ref>{{cite web|url=http://www.revenuel.com/canonical-issue-solution-tag/|title=Canonical Issue and How to Use Canonical Tag – The Proper Way|last1=Biswas|first1=Kushal|date=|website=|publisher=RevenueI|archive-url=https://web.archive.org/web/20160614052029/http://www.revenuel.com/canonical-issue-solution-tag/|archive-date=14 June 2016|accessdate=18 June 2015}}</ref><ref>{{cite web|last1=Zadro|first1=Dario|title=Rel=Canonical - A Beginners Guide to Canonical Tags - Where and When to Use Them|date=19 February 2015 |url=https://zadroweb.com/a-beginners-guide-to-canonical-tag/|publisher=Zadro Web|accessdate=18 June 2015}}</ref>

In February 2009, [[Google]], [[Yahoo]] and [[Microsoft]] announced support for the <code>canonical</code> link element, which can be inserted into the [[HTML element#head|{{tag|head|o}} section]] of a web page, to allow webmasters to prevent these issues.<ref>{{Cite web|url=https://searchengineland.com/canonical-tag-16537|title=Google, Yahoo & Microsoft Unite On "Canonical Tag" To Reduce Duplicate Content Clutter|last=Fox|first=Vanessa|authorlink=Vanessa Fox|date=2009-02-12|website=|publisher=[[Search Engine Land]]|archive-url=|archive-date=|accessdate=2012-08-02}}</ref> The canonical link element helps webmasters make clear to the search engines which page should be credited as the original.

== How search engines handle <code>[[Link relation|rel]]=canonical</code> ==

Search engines try to utilize canonical link definitions as an output filter for their search results. If multiple URLs contain the same content in the result set, the canonical link URL definitions will likely be incorporated to determine the original source of the content. "For example, when Google finds identical content instances, it decides to show one of them. Its choice of the resource to display in the search results will depend upon the search query."<ref>How Google And Other Search Engines Manage Canonical Links | http://seomediax.com/seo/how-google-and-other-search-engines-manage-canonical-links/</ref> {{citation needed|date=October 2018}}

According to Google, the <code>canonical</code> link element is not considered to be a directive, but rather a hint that the ranking algorithm will "honor strongly."<ref name="googleblog"/><ref>{{Cite web|url=https://support.google.com/webmasters/answer/139066#2|title=Consolidate duplicate URLs - Search Console Help|website=support.google.com}}</ref>

While the canonical link element has its benefits, [[Matt Cutts]], then the head of Google's [[Spamdexing|webspam]] team, has said that the search engine prefers the use of [[301 redirect#HTTP status codes 3xx|301 redirects]]. Cutts said the preference for redirects is because Google's [[Web crawler|spiders]] can choose to ignore a canonical link element if they deem it more beneficial to do so.<ref>{{Cite web|url=https://www.mattcutts.com/blog/rel-canonical-html-head/|title=A rel [equals] canonical corner case|last1=Cutts|first1=Matt|authorlink=Matt Cutts|date=2011-05-16|website=|archive-url=|archive-date=|accessdate=2012-08-02}}</ref>

== Implementation ==
=== Semantic tag ===
The canonical link element can be either used in the [[Semantics (computer science)|semantic]] HTML {{tag|head|o}} or sent with the [[HTTP header]] of a document. For non HTML documents, the HTTP header is an alternate way to set a canonical URL.<ref name="Audisto GmbH"/><ref>{{Cite web|url=https://support.google.com/webmasters/answer/139066#6|title=Consolidate duplicate URLs - Search Console Help|website=support.google.com}}</ref>

By the HTML 5 standard, the <syntaxhighlight lang="html" inline><link rel="canonical" href="http://example.com/"></syntaxhighlight> HTML element must be within the {{tag|head|o}} section of the document.<ref>{{Cite web|url=https://www.w3schools.com/tags/tag_link.asp|title=HTML link tag|website=www.w3schools.com|access-date=2019-01-07}}</ref>

=== Self-hyperlink ===
Some sites such as [[Stack Overflow]]<ref name=link_itself>{{cite web |title=Why does the question title link to itself on the answer page? |url=https://meta.stackexchange.com/questions/47653/why-does-the-question-title-link-to-itself-on-the-answer-page/325170 |website=Meta Stack Exchange |date=2010-04-23}}</ref> have on-page [[hyperlink]]s which link to a [[clean URL]] of themselves. [[Usability]] benefits are facilitating copying the [[hyperlink]] target URL or title if the browser or a [[browser extension]] offers a "Copy link text" [[context menu]] option for hyperlinks, the ability for the original URL to be retrieved from a saved page if not stored by the browser into a comment inside the file, as well as the ability to duplicate the opened page into a new tab right next to the currently opened one if the browser lacks such a feature.<ref>{{cite web |title=3 FireFox Addons to Easier Copy Links and Anchor Texts |url=https://www.searchenginejournal.com/3-firefox-addons-to-easier-copy-links-and-anchor-texts/26742/ |website=Search Engine Journal |language=en |date=7 January 2011}}</ref><ref name=link_itself/>

==Examples==

=== HTML ===
Below is an example of HTML code that uses the {{mono|1=rel=canonical}} inside the {{tag|head|o}} tag. The code could be used on a page, such as <syntaxhighlight lang="html" inline="">https://example.com/page.php?parameter=1</syntaxhighlight>to tell search engines that the <syntaxhighlight lang="html" inline="">https://example.com/page.php</syntaxhighlight> is the preferred version of the webpage.<syntaxhighlight lang="html">
<!DOCTYPE html>
<html>
<head>
<link rel="canonical" href="https://www.example.com/page.php">
</head>
<body>
...
</body>
</html>
</syntaxhighlight>

=== HTTP ===
<syntaxhighlight lang="http">
HTTP/1.1 200 OK
Content-Type: application/pdf
Link: <https://www.newthink.life/page.php>; rel="canonical"
Content-Length: 4223
...
</syntaxhighlight>

==See also==
* [[URL normalization]]

==References==
{{Reflist}}

{{DEFAULTSORT:Canonical link element}}
[[Category:Search engine optimization]]
[[Category:HTML]]
{{Навигационная таблица/Портал/Английская Википедия}}
[[Категория:Английская Википедия]]
[[Категория:Википедия]]
[[Категория:Статья из Википедии]]
[[Категория:Статья из Английской Википедии]]

Английская Википедия:Canonical link element - История изменений